1. Field of the Invention
This invention relates generally to manually operated automotive transmissions and more particularly to the cluster gear and input shaft arrangement of such transmissions.
2. Description of the Prior Art
In the operation of manual transmissions for automotive vehicles, a condition called rollover rattle has been identified in which noise associated with engine idle speed variations is produced. The noise associated with this condition rises while the clutch that selectively, driveably connects the engine to the input shaft of the transmission is engaged and the gear shift lever is moved to the neutral position, where none of the forward or reverse gears are engaged, and the engine is running at normal idle speed. Minor variations in the idle engine speed cause the gears on the cluster shaft and the pinions on the countershaft, with which the cluster shaft gears are continually engaged, to contact each other alternately on opposite lateral faces of the meshing teeth. The speed variations cause a minor amount of impact as the normal angular clearance between the meshing teeth is taken up due to the contact being made on opposite faces, rather than continuously on one face of the meshing teeth. The drive perceives this condition as a rattling sound emanating from the transmission.
Manual transmissions produce also another gear rattle noise that arises while the engine operates at light throttle conditions, where the vehicle speed is approximately 25 mph, and the transmission in one of the higher forward speed ratios, such as fourth gear. When these conditions are present, transmission produce an unwanted rattle that is offensive to the operator and the passengers.
Various attempts have been made to reduce or eliminate the noise associated with these conditions. For example, devices mounted on the cluster gear adjacent one of the gear wheels have been used to apply continuously a resilient force to a toothed wheel so that it maintains constant contact with both faces of a meshing gear teeth during operation of the transmission. Devices of this type are used to overcome rattle by preventing the impact that results when engine speed variations cause impact on opposite lateral faces of the gear teeth.
Other means, such as by changing the spring rate of the spring damper located on the neutral clutch that connects the engine crankshaft to the input shaft of the transmission, have been used to tune the vibrations of the driveline particularly those vibrations associated with torsional response.